So picking up on recent points, has this something to do with how the composer originally wrote the music. What I mean is that if a composer was writing for an instrument with a set range of notes then the key he chose to write in would impact on the distribution of note above and below the key note that he had to work with, which could (would) influence the tune that they finally came up with.
I don't believe so. C minor is a dark key with many composers across the periods writing their darkest works in that key - Beethoven, Shostakovich, to name only two. These pieces were written for a variety of instruments - and how the strings resonate while stopped, or in relation to the volume of air in the body are effects that don't link with how it lies on a piano, or on a transposing instrument. For the clarinet, there are weak notes right next to resonant notes, and changing from Bb clarinet to A clarinet will change how this responds, but not how the piece sounds and the impact of the key.
Rightly or wrongly what we are talking about is the characteristics of a key. This changes from person to person to a large extent, and also covers a range of pitch changes - so I can see that believing that the keys have retained a universally felt characteristic is difficult to get your head round. A lot of churches into gospel music tend to like Db - which is very close to C in pitch - but clearly a different emotion for them. It just makes life a bit more interesting. I don't claim any ability to recognise keys by ear, but I do appreciate the intent of a composer choosing that key.
